Calutron receivers



E. J. LOFGREN 2,851,607

CALUTRON RECEIVERS Sept. 9, 1958 Filed Aug. 29, 1945 4 Sheets-Sheet 1 I N V EN TOR. fan 4R0 J ZOFGRf/V BY Mam Sgpt. 9, 1958 E. J. LOFGREN CALUTRON RECEIVERS 4 Sheets-Sheet 2 Filed Aug. 29, 1945 Sept. 9, 1958 E. J. LOFGREN CALUTRON RECEIVERS 4 Sheets-Sheet 3 Filed Aug. 29, 1945 INVENTOR. OW/4K0 J Z OFGRE/V BYY - ATTORNEY 55am. 9, 1958 E. J. LOFGREN CALUTRON RECEIVERS 4 Sheets-Sheet 4 Filed Aug. 29, 1945 INVENTOR. [DWARD J ZOFGRE/V United States Patent CALUTRON RECEIVERS Edward J. Lofgren, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application August 29, 1945, Serial No. 613,359

5 Claims. (Cl. 250-413) The general subject of this invention involves the separation, based on difference in mass, of minute particles, such as atoms, and especially the separation of isotopes of an element, or the separation of a portion of an element enriched with respect to a particular isotope on a scale yielding commercially useful quantities of the collected material.

The type of means or mechanism to which the invention relates is known as a calutron, and correspondingly the method or process is known as a calutron method or process. The presently preferred form of the calutron includes an evacuated chamber mounted in a magnetic field and containing apparatus for ionizing a polyisotope to be treated, apparatus for projecting a beam of ionized particles of the polyisotope along paths determined by the masses of the respective ions, and a target apparatus for deionizing the particles of the beam and for retaining at least one selected isotope component in a separated region from which it can be recovered.

For a complete disclosure of a calutron and of its mode of operation, reference is made to the copending application of Ernest 0. Lawrence, Serial No. 557,784, filed October 9, 1944, for Methods of and Apparatus for Separating Materials, now Patent No. 2,709,222, granted May 24, 1955. The form of calutron disclosed in that application comprises an evacuated tank placed between the poles of an electromagnet so that the evacuated space within the tank is pervaded with a substantially uniform magnetic field of high flux density. Within the tank there is provided a source unit that includes means for supplying the polyisotope as a vapor or gas to an ionizing region, ionizing apparatus for producing positively ionized particles from the vapor, and an accelerating device maintained at a high negative electrical potential with respect to the ionizing apparatus for withdrawing the positive ions and imparting to each of them a predetermined energy in the form of substantially uniform velocities along paths generally normal to the direction of the magnetic field toward an elongated beam defining slit in the accelerating device disposed generally parallel to the direction of the magnetic field.

The accelerated ions move transversely to the magnetic field and are constrained to travel along arcuate paths having radii that vary with the masses of the particles. By virtue of the accelerating slit construction, the paths for the ions of a given mass diverge from a median path to an extent determined by the geometry of the ionizing and accelerating devices. This divergence of the paths of travel of the ions of a given mass continues through the first 90 of arcuate travel, and then the paths converge during the next 90 and cross each other in a region of focus approximately 180 from the source unit. Thus, in effect, geometrical focusing of a ribbon-shaped stream of ions of a given mass is accomplished adjacent the 180 point, even though there is a relatively wide angle of divergence of the ions at their source. The paths of a stream of ions of a given mass do not all cross pre- "ice paths that define a ribbon-shaped stream coming to a focus having an elongated rectangular pattern at approximately from the accelerating apparatus. Being respectively composed of ions of different masses, the streams of ions of different isotopes have mean radii of curvature that dilfer by an amount dependent solely upon the mass difference of their respective constitutent ions. As a result, the centers of the foci of the streams of different isotopes are spaced apart by an amount approximately equal to the ditference in the diameters of their respective median paths. In the case of the heavier elements, such as uranium, the difference in mass between the isotopes is not sufiicient for accomplishing complete separation of the streams in which the ions of the different isotopes respectively travel, while employing a practical minimum divergence of the beam at the beam defining slit, and a'plurality of overlapping streams having overlapping regions of focus are treated.

A receiver is disposed Within the vacuum tank adjacent the 180 foci of the isotope ions to be separated, for

deionizing them and for separately collecting one or all of them as may be desired. Because of the necessary overlapping of the streams at their foci, it is impractical in one operation to separate completely the isotopes of the heavier elements, and, in practice, the separated quantities of material collected at the receiver are merely enriched with respect to a particular isotope.

If the initial divergence of the ion paths at the beam defining slit is increased in order to transmit a greater number of ions, the width of the elongated rectangular focal pattern of each isotope stream is increased, and the mutual overlapping of two streams of ions of different isotopes at their regions of focus is increased by an amount approximating the combined increases in the Widths of their focal patterns. Thus, the obtainable degree of enrichment of collected material with respect to a particular isotope decreases as the amount of material transmitted in the beam is increased, and a compromise has heretofore been required between maximum production and maximum enrichment.

In order to increase the quantity of material transmitted in an ion beam without reducing the isotopic enrichment of the collected material, the shape or configuration of the beam may be distorted by means of specially contoured bodies of magnetically permeable material that are introduced into the calutron tank for distorting the magnetic field traversed by the beam. Such magnetically permeable bodies are referred to as magnetic shims, and the resulting distorted beam is referred to as a magnetically shimmed beam or a shimmed beam. In a copending application of Julius Robert Oppenheimer et al., Serial No. 637,690, filed December 28, 1945, now Patent No. 2,719,924, granted October 4, 1955, an arrangement of magnetic shims is disclosed, and the configuration of the distorted beam resulting from the use of the shims is illustrated and described in some detail. As disclosed in that application, the distortion of the beam is such that the normally elongated, rectangular focal pattern of each beam component is compressed along one side and is extended along the opposite side and, in addition, is curved to produce what may be termed a gull-wing pattern.

By distorting the focal patterns in this manner, the average width of the pattern for each isotope ion stream is reduced, and the length thereof is increased, whereby the amount of overlapping of the streams of diiferent isotopes is substantially reduced for any given initial angular divergence at the source. This permits increasing the amount of material transmitted by employing a greater initial angular divergence without producing a corresponding reduction in'the isotopic enhancement of the separated material collected'by the receiver.

Because of the manner in which the shimmed beam is distorted, the distribution of material is far from uniform along the lengths of the focal patterns, and the ion density diminishes very substantially toward the ends of the patterns. This complicates the problem of designing slots in a receiver face plate for passing the optimum portions of the beam to a collecting chamber.

It is an object of the present invention to provide an improved calutron receiver adapted to collect a desired portion of the material transmitted in a magnetically shimmed ion beam.

Another object of the invention is to provide a calutron receiver adapted to collect material from one isotope ion stream of a magnetically shimmed ion beam in a manner permitting separate recovery of dilferent portions of the collected material according to the positions they occupied in the beam adjacent the 180 region of focus.

Further objects and advantages of the invention will appear from the following description of a preferred embodiment thereof and from the accompanying drawplane of the section being indicated by the line 3--3 in Fig. 2; and

Fig. 4 is an elevational view of the receiver, looking at the beam receiving face thereof, certain parts being broken away to show the interior of thereceiver.

Referring to the drawings, Fig. 1 illustrates a calutron .of the general character disclosed in the Lawrence application, mentioned above, but embodying certain modifications including, among other features, a receiver constructed in accordance with the present invention for receiving a magnetically shimmed beam. The. calutron comprises a C-shaped tank 10 that is support-ed midway between a pair of horizontally disposed, vertically spaced apart pole faces 11 (only one being shown) of acalutron magnet, whereby a magnetic field may be created throughout the interior of the tank with the magnetic lines of force passing upwardly therethrough. Thetank is adapted to be evacuated through a pumpout conduit 12 to reduce the interior pressure, in a manner-disclosed in the above-mentioned Lawrence application, and is provided with magnetic shims (not shown) for distorting an ion beam passing through the tank, in the, manner and for the purpose disclosed in the above-mentioned Oppenheimer et al. application.

. A source unit, illustrated schematically in Fig. 1 and generally designated 13, is mounted within the tank 10 at one end thereof on one of a pair of removable end walls 14 for producing, from a polyisotopic-charge material, a beam of singly ionized positive. ions traveling alongsubstantially arcuate paths to a region of focus approximately 180 along said paths toward the opposite end of the tank. As hereinbefore indicated, the source unit may be designed to project the ions along paths that are initially divergent to either side of a median path by various angles between predetermined maxima and that later converge toward and diverge beyond a; region of focus at angles'on either side of amedian path-dependent upon their respective initial angular divergences and the efliects of the distorted magnetic field.

The paths of several ions are schematically and somewhat ideally illustrated in Fig. 1 by two sets of three lines each, one set representing a median path 15 and two extreme paths 16 and 17 of a stream of ions of one isotope, and the other set representing a median path 18 and two extreme paths 19 and 20 of a stream of ions of another heavier isotope. The stream of ions represented by the first-mentioned set of lines 15, 16 and 17 converges toward and diverges beyond a focus 21 located approximately 180 from the source unit 13 toward the opposite end of the tank 10, and, similarly the stream of ions represented by the second-mentioned set of lines 18, 19, and 20 converges toward and diverges beyond a second focus 22 that is laterally spaced from the region of focus 21 of the ions of a lesser mass. Fora disclosure of the actual shape of vthe portion of the beam comprised by the two streams of different isotopes (ignoring all scattered material), reference is made to the above mentioned Oppenheimer et a1. application.

A receiver, generally designated 25, is mounted on a removable end wall 14 of the C-shaped tank 10, at the opposite end thereof fromthe source unit 13, for collecting and deionizing ions arriving at one of the foci 21 separately from those' arriving at the adjacent focus 22, and for trapping ions reaching the first-mentioned focus 21 in such manner that-they can be separately removed from the calutron.

The receiver 25 is mounted on a tube 26 that projects outwardly through an aperture 27 in the adjacent end wall14 of the tank 10. The tube 26 is preferably supported in the aperture 27 on apparatus carried by a cylindrical insulator 28 secured in an air-tight manner around the aperture, the tube being preferably mounted for rotary movement about its own axis, for pivotal movement in both a horizontal and vertical direction, and for longitudinal movement along its axis, with the outer end of the tube 26 and the space between the tube and the surrounding walls of the aperture 27 and insulator 28 suitably sealed against leakage of air into the tank. The apparatus for supporting the tube 26 forms no part of the present invention, andone example of suitable apparatus is disclosed in detail in theabove-mentioned Lawrence application. With such apparatus, the inner end of the tube 26 may be rotated and translated in any direction for aligning the receiver 25 with the beam to be received thereby.

The receiver 25 comprises a back plate 30 of rectangular configuration, having a centrally disposed aperture 31 therein. The inner end of the supporting tube 26 is secured to the back plate 30, in coaxial alignment with the aperture 31, --by means of a flange 32 that may be soldered to the tube and removably secured to the back plate 30 by suitable fastening means 33. A housing projects forwardly from the back plate 30 and comprises a pair of oppositely disposed side plates 34 and a pair of oppositely disposed end plates 35 that are suitably secured to each other and to the back plate 30.

Two rows of angle brackets are respectively secured to the inner surfaces of the side plates 34 along lines parallel to and spaced from the forward edges of the side plates. Each angle bracket 40 carries a forwardly projecting stand-off insulator 41 of ceramic material or the like, and a rectangular face plate 42 is mounted on the insulators 41 to close the forward end of the receiver housing except for a small gap provided for electrical insulation purposes between the face plate and the side plates 34 and end plates 35.

The face plate 42 is provided with a large, centrally disposed, generally rectangular. opening 43 therethrough, and the opening 43 is closed by a beam defining plate 44 secured to the back pside of the face plate, except for slots provided therein to pass selected delimited portions of the ion beam to the interior of the receiver housing. The

graphite, is provided with two sets of curved beam defining slots 45 and 48 therethrough, each set of slots comprising, in eflfect, portions of a single elongated slot conforming in shape to the focal pattern of the isotope ion stream to be passed thereby, the portions being longitudinally spaced apart for passing three longitudinally separated fragments of the isotope ion stream. The respective centerlines of the two sets of slots 45 and 48 are spaced apart an amount equal to the lateral space between the longitudinal center lines of the focal patterns of the two isotope ion streams to be received.

A collecting pocket, generally designated 50, for receiving and retaining ions admitted through the set of slots 45, is positioned inside the receiver housing and is supported in place by a number of stand-01f insulators 51 that are mounted on a plate 52, in turn mounted on a pair of bars 53. The bars 53 extend transversely of the receiver housing between the side plates 34 and are secured thereto at their opposite ends by suitable fastening means 54. The pocket 50 comprises a channel-shaped member 55 that extends in both directions beyond the extreme ends of the set of slots 45 in the beam defining plate 44, and the channel in the member 55 is closed at its opposite ends by a pair of end plates 56 secured to the member 55 in any suitable manner, as by soldering. A cover plate 57 is removably secured to the edges of the channel member 55 and of the end plates 56 by suitable fastening means 59, and is provided with an elongated, substantially arcuate opening 58 that is aligned with the set of slots 45 for admitting into the pocket 50 ions passing through the aligned set of slots.

The pocket 50 is provided with three liner compartments 60, 61, and 62, each liner compartment being closed on all sides except for openings 63, 64, and 65 therein, respectively, the opening in each liner compartment being aligned with an adjacent portion of the opening 58 in the cover plate 57 and conforming thereto in size and configuration. The liner compartments may be made of sheet metal, preferably sheet copper, and are provided with oppositely disposed, outwardly projecting flanges 66 that are adapted to be clamped between the pocket cover plate 57 and a pair of supporting bars 67 for holding the liner compartments firmly in place. The supporting bars 67 may be secured to the inside of the channel member 55 adjacent the edges thereof in any suitable manner, as by soldering.

An electrical contact 68 is secured to the back of the channel member 55, and an electrical lead from the contact 68 is carried out of the calutron tank through the supporting tube 26. A tubular insulator 69 may be mounted in an aperture in the plate 52 to permit the electrical lead to pass therethrough without being shorted to ground through the receiver framework.

A second collecting pocket, generally designated 72, is positioned inside the receiver housing immediately behind the set of slots 48 for receiving and retaining ions passing therethrough. The pocket 72 extends in both directions beyond the extreme ends of the associated set of slots in the beam defining plate 44, and is longitudinally similarly curved from end to end to follow the contour of the slots. This pocket 72 is preferably made of graphite and may comprise an ion intercepting member 73 and a trapping member 74 shaped to define a collecting chamber 75 having an entrance slot 76 therein aligned with the set of slots 48 in the beam defining plate 44. The ion intercepting member 73 and the trapping member 74 may be secured together and to a supporting bracket 77 with suitable fasting means 78, and the supporting bracket 77 is in turn supported by a number of insulators 79 carried by a plate 80 secured to an adjacent side wall 34 of the receiver housing with suitable fastening means 81.

Since the receiver absorbs a considerable amount of energy as a result of bombardment by ions traveling in the ion beam, it is highly desirable to cool the parts most heavily bombarded. When employed for the intended purpose of receiving a uranium ion beam to collect the U isotope in the large pocket 50 and the U isotope in the small pocket 72, the parts of the receiver most heavily bombarded are the face plate 42 and the small collecting pocket 72. To cool the face plate 42, a cooling fluid line is run into the interior of the receiver housing through the supporting tube 26 and is secured to the back side of the face plate 42, in heat conducting relation thereto, around three sides of the beam defining plate 44 and then out of the receiver housing again through the supporting tube 26, whereby a suitable cooling fluid may be circulated through the tube to cool the face plate 42.

To cool the small collecting pocket 72, a cooling fluid line 86, consisting of a pair of concentric copper tubes that define a pair of parallel passages 87 and 83, is run into the receiver housing through the supporting tube 26 and is secured to the supporting bracket 77, in heat conducting relation thereto, along the full length thereof. The cooling fluid line 86 terminates inside the receiver housing in a squirt tube type of interconnection between its concentric passages 87 and 88, whereby a coo-ling fluid may be brought into the receiver through the outer passageway 87 and returned to the source of supply through the inner passageway 88, for cooling the supporting bracket 77 and the associated collecting pocket 72, in a manner similar to that disclosed in my co-pending application, Serial No. 596,222, filed May 28, 1945, now Patent No. 2,745,965, granted May 15, 1956.

The use of an electrically nonconducting cooling fluid, such as distilled water, permits the cooling fluid line 86 to serve as an electrical lead to the small collecting pocket 72 for measuring the quantity of ions striking the ion intercepting member 73, and permits the cooling fluid line 85 to serve as an electrical lead to the face plate 42 and the beam defining plate 44 for measuring the quantity of ions intercepted thereby, without shorting these parts to ground through the cooling fluid supply system.

In order to prevent contamination of the interior of the liner compartments 60, 61, and 62 of the large collecting pocket 50 during the warm-up period, before the beam to be received has become stabilized and has been focused for reception, a door 90 is mounted on the front of the face plate 42 by means of a pair of hinges 91. The door is slightly greater in length than the two sets of slots 45 and 48 in the beam defining plate 44 and is adapted to swing about the hinges 91 from a closed position against the face plate, covering the two sets of slots 45 and 48, to an open position out of the paths of the U+ portions of the ion beam, as best shown in Fig. 2.

For operating the door between its open and closed positions, a rod 92 is pivotally connected to the door by means of a bracket 93 and projects into the interior of the receiver through an aperture 94 in the face plate 42. One end of a length of heavy wire 95, such as music wire, is suitably secured to the opposite end of the rod 92 by fastening means 96, and the wire extends from the rod 92 out of the receiver and into the supporting tube 26. A length of copper tubing or the like 97 surrounds the wire 95 for a considerable portion of its length and is bent to conform to a desired path of travel for the wire, whereby electrical contact between the wire and other parts of the receiver may be avoided. Inside the supporting tube 26, a suitable mechanism (not shown) may be provided, such as that disclosed in Patent No. 2,745,965 mentioned above, for moving the wire 95 within the tubing 97 to swing the door 90 about its hinge 91 between open and closed positions.

To facilitate determining when the ion beam is properly focused for most eflicient reception, a narrow slot 100 is provided in the door 90 in alignment with the center one of the set of three slots 48 when the door is in its closed position. Thus, when the door 90 is closed,

' the slot 100 is adapted to pass a narrow portion of the lines 85 and 86, and'with the door 90 in its closed position, the beam is created and focused in accordance with the current to the small collecting pocket 72 resulting from the passage of ions through the slot 1% thereto.

When a proper focus of the beam has been achieved, the door 90 is opened, and subsequent readings of current to the small collecting pocket 72 and to the large collecting pocket 50 may be observed as a check on general beam conditions and on the rate at which ions are entering the two pockets. The door 90 may be closed during a run in the event the condition of the beam should become unfavorable, in order to prevent contamination of the material in the pocket 60 while the condition of the beam is being corrected; or the door may be closed at regular intervals during a run to obtain a more reliable check on the accuracy of focus and to carry out any required refocusing operation.

At the conclusion of a run, the beam is cut' off, the circulation of cooling fluid through the cooling fluid lines is stopped, the pressure in the tank is brought up to atmosphere pressure, andthe receiver is removed from the tank by removing the tank wall 14 on which it is mounted. Access to the interior of the receiver is obthe face plate 42 for separate recovery of the beam components deposited therein.

By separately analyzing the material collected in the three liner compartments 6%, 61, and 62, information may be obtained as to the distribution of material over the cross sectional area of the U portion of the beam at its region of focus, and in the event that the isotopic enrichment of material collected from the center of the focal pattern of this portion of the ion beam differs substantially from the enrichment of the material collected adjacent the ends of the focal pattern, it may be desired to segregate the materials from the three pocket-liners, depending upon the contemplated uses for such materials.

When the receiver described herein is to be employed in a calutron fed with a U enriched charge material, for producing material still more highly enriched with the U isotope, it may be desirable to wash out the calutron tank and most of the apparatus therein to recover material deposited thereon for recycling. In such cases the enrichment of the material to be recycled is increased by trapping in the small collecting pocket '72 the maximum possible amount of the U isotope and removing the trapped U material from the tank before performing the washing operation.

While I have described in detail a specific embodiment of my invention, it is to be understood that this has been done for illustrative purposes and that the scope of my invention is not limited thereby except as required by the appended claims.

8 What is claimed is: 1. In a calutron having means for transmltting an ion beam through a magnetic field in a direction generally normal to its magnetic lines of force toward a region of focus,-an ion receiver comprising beam delimiting means disposed in the path of the beam adjacent the region of focus for passing a delimited portion of the beam, and an elongated collecting pocket disposed to receive ions passed by the beam delimiting means, said pocket being substantially aligned longitudinally with the magnetic lines of force and being transversely partitioned into a plurality of compartments respectively defined by a corresponding plurality of separately removable liner elements.

2. In a calutron having means for transmitting an ion beam through a magnetic field in a direction generally normal to its magnetic lines of force toward a region of focus, an ion receiver comprising beam delimiting means disposed in the path of the beam adjacent the region of focus for passing a delimited portion of the beam, and an elongated collecting pocket disposed to receive ions passed by the beam delimiting means, said pocket being substantially aligned longitudinally with the magnetic lines of force and being transversely partitioned into at least three compartments respectively defined by three separately removable liner elements.

3. In a calutron having means for transmitting an ion beam through a magnetic field in a direction generally normal to its magnetic lines of force toward a region of focus, an ion receiver comprising beam delimiting means disposed in the path of the beam adjacent the region of focus for passing a delimited portion of the beam, and an elongated collecting pocket disposed to'receive ions passed by the beam delimiting means, said pocket being substantially aligned longitudinally with the magnetic lines of force and including an elongated case housing a plurality of liner elements that transversely partition the case into a'corresponding plurality of separately removable ion receiving compartments.

4. In a calutron having means for transmitting an ion beam through a magnetic field in a direction generally normal to its magnetic lines of force toward a region of focus, an ion receiver comprising beam delimiting means disposed in the path of the beam adjacent the region of focus for passing a delimited portion of the beam, and an elongated collecting pocket disposed to receive ions passed by the beam delimiting means, said pocket being substantially aligned longitudinally with the magnetic lines of force and including an elongated case housing a plurality of liner elements that transversely partition the case into at least three separately removable ion receiving compartments.

5. In a calutron having means for transmitting an ion beam through a magnetic field in a direction generally normal to its magnetic lines of force toward a region of focus, a face plate having a plurality of enlongated slots therein disposed in longitudinal alignment in the path of the beam adjacent the region of focus for passing a delimited portion of the beam, an elongated pocket disposed to receive ions passed by the slots, said slots and pocket being substantially aligned longitudinally with said magnetic lines of forces, and said pocket being transversely partitioned in a plurality of compartments defined by separately removable liner elements so that there is one compartment for each of said slots.

References Cited in the file of this patent UNITED STATES PATENTS Hipple Oct. 5, 1943 Hoover Feb. 15, 1944 OTHER REFERENCES 

